Process for bleaching cellulose fiber



Patented Apr. 21, 1931 I I UNITED sTA'rss PATENT OFFICE ERICK OIPIEBMANN', 01' B EBLIN, GERMANY, ASSIGNO: TO I. G. FABBENWDUSTBIE AKTIENGESELLSCHAFT, OI IBANKFOBT-ON-TBE-MAIN, GERMANY ZPBOGESS FOR BLEACHING CELLULOSE FIBER Io Drawing. Application filed April 14,1925, serial No. 28,145, and in llermany Kay 22, 1924.

This invention relates to a certain new and to a weak preliminary bleaching in the usualuseful process for bleaching chemical pulp way before starting the final bleaching with or any cellulose fiber to make it specially the weak caustic alkali or the molecular useful as a rawmaterial for artificial silk equivalent quantity of hydroxide of an alkali spinning solutions although it may be used formin metal. 55

for many other purposes. The ollowing example will show the quan- Processes are known for the bleaching of tities and reagents for ableaching unit. 3000 cellulosefiber by means of alkaline bleaching kg. of fiber pulp capable of being bleached solution, amon stothers, sodium and calcium are preliminarily bleached with about 70 hypochlorite, or the express purpose of obkg. chloride of lime in the form of a cal- 60 taining pure white products. This, however, cium hypochlorite solution; it is washed out has hitherto taken place at the expense of and I then add thereto. about 40 kg. of caustic the fiber, whilst greatly increasing the copper soda and bleach with 200 kg. chloride of lime. m'imber and also its solubility in a solution The pulp remains weakly alkaline to the end P of caustic soda or of sodium sulfide. The alofthe bleaching andthe result is a clear white as kalinit of the usual bleaching liquors does cellulose with a. very low copper number .not ce to maintain the alkaline. reaction (about 1%{) and high' ercentage of alpha during the courseof. the bleaching. v cellulose (a out 88-90%.

This invention starts from the fact that If the preliminary bleaching is omitted the q with quite small additions of caustic alkall, addition of caustic soda will be increased ao- 10 for example one percent, reckoned on the cor-din to the increased consumption of quantity of cellulose, in combinatlon wlth chlori e of limefor the alkaline phase of the the usual chloride of lime or sodium hypobleachin chlorite bleach, there produced a 091 1 Instead of caustic soda it is possible to use pithe purest Wh10h s 1: ards the hydroxide of any alkali forming metal, 75 its other quahties, also complies Wlt the including magnesium, in the "molecular highest requlrem nts, 1n partloular t (1088 equivalent proportion. This means that not exceed F PP h of about 0116 caustic soda is taken as a basis and the quanl-c t While hg t0 the usual tity ofother alkali forming hydroxides when A leach, 1ng processes, constituent parts solub e used, is reckoned therefrom. This, about so in s'odlum sulfide remain m a ratio of from 1% of caustic soda based on the amount of 12 to 15 P 111 the bleachmg fiber, the cellulose is an advantageous quantity. If products according to the new process Show calcium hydroxide is used in lace'of causat most a solublhty of fmm $13,110 111119 P tic soda, the amount taken will be such as fient- The lhmhtenance 1 defimte p to give a basicity to the solution corresponda5 ures s c as 15 me I e known P ing to the basicity given by the use of-1% e l not necessary fl case of the new of caustic soda. It.is likewise possible to pro s a combine the use of calcium hypochlorite or The Process maybe earned out l e y any other 'hypochlorite with the use of adding to the fiber pulp from 0- i on P calcium hydroxide or any other hydroxide 96 cent, of its weight of caustic alkali or the f th lk li f mi t l i l di molecular equivalent quantity of hydroxides i A11 bi ti m y ba g d, ofalkali forming metals and then supplymg H in now ti fl l d ib d d y the bleaching liquor, r by m g the abQVe ascertained the nature of my said invention mentioned amount of alkali with the bleachd i wh t manner the same is to be per- 95 ing liquor before treatmg the fiber p p formed, I declare that what I claim is: h r w It is Stated a in thls y the 1- The process of bleaching cellulose which liquor maintains its alkaline reaction right comprises adding aboutl per cent of an agent 50 up to the termination of the bleaching. selected from the group consisting of caustic It is also possible to subject the fiber pulp alkali and hydroxides of alkaline earth metals l ll liminar bleaching with and magnesium, and thereupon applying bleaching liquors thereby obtaining a product of purest whiteness, having a copper number not exceedin about 1 per cent, and having at the most a out 6 to 9 er cent of constituents soluble in sodium de.

' 2. The process of bleaching cellulose which comprises subjecting cellulose to a weak prea hypochldrite bleaching agent, freeing the cellulose from the h pochlorite and thereafter finishing the bleaching with a hypochlorite bleachliquor containi'n an addition of 0.8 to 1' per cent, calculatef of an agent selected from the group consist ing of caustic alkali and hydroxides of alkaline earth metals and magnesium, which addition of a small amount of an alkaline acting agent serves to keep the bleach liquor distinctly, but weakly, alkaline during the finishin bleaching step, thereby obtaining a bleached cellulose of purest whiteness, having a copper number not exceeding about 1 per cent and having at the most about 6 to, 9

per cent of constituents soluble in sodium sulfide.

In testimony whereof I have signed my name to this specification.

' DB. ERICH OPFERll IANN.

on the quantity of the cellulose, 

